Frequency drift compensator



Filed March 15, 1937 Patented Sept. 5, 1939 i UNITED STATES PATENT OFFICE FREQUENCY mumoomcuss'ron John Kelly Johnson, Chicago, 111., assignor to Wells-Gardner & Company, Chicago, 111., a corporation of Illinois Application March 15, 1937, Serial No. 130,945

Claims. (Cl. 175-415) The circuits of radio receiving sets have a by means of a belt l4. The disl: I2 is composed tendency to drift in frequency response due to preferably of brass and invar. Soldering lugs variations in temperature which cause shifts in i5 and I6 are held in costact with the disks H frequencies in tuning condensers or coils, in diand i2, respectively, by this bolt, the disk H and 5 electric constants, and in power factors of var lug I 5 being suitably insulated from the bolt 5 ions insulating materials. by means of an insulating tube l3 and an in- These produce a very substantial frequency sulating washer i8. drift which causes difliculty in tuning particu- The dielectric disk i3 is made of a composilarly when the receiving set is equipped with tion containing rubber and is substantially unan automatic tuning device such as the tele affected by moisture conditions and the washer 10 phone dial which returns the tuning condensers i8 is covered with a suitable wax E9 to the depth of the several stages to a definite predetermined of about 6 of an inch so that it is also subsetting for a desired broadcasting station. in stantially impervious to moisture. this case it becomes necessary to provide means The disks i! and it are normally slightly refor insuring that a given setting of the tuning versely arched, out this archin is purposely ex- 15 condensers corresponds to a given radio ireaggerated in the drawing in order to make this quency in order that the set may be properly point evident. The shape of the disk ii will tuned for the desired station at all temperabe substantially constant at temperatures tures to which the set is lilgeiy'to besubjected. such as will he usually encountered by a radio 2Q An object of this invention is to provide means receiving set, but the bimetal dish i? will change for compensating for variations in temperature its curvature with variations in temperature. whereby the receiving set will not drift materi- These changes in the degree of curvature of the ally at any point within'its range from a prededisk l2 produce variations in the capacity of the termined setting. condenser and the variations in the capacity thus Thisand other objects as will hereinafter approduced in the compensating capacitor are pear are accomplished by this invention which so chosen as to substantially balance the changes is fully described in the following specification in capacity of the-parts of the oscillator circuit and shown in the accompanying drawing in of the radio receiving set in which it is used.

which the figure is an enlarged section through Thus it has been found by actual test that by a condenser used to automatically compensate the use of such a compensating capacitor, the 36 for changes in the set clue to temperature. frequency drift of the set due to capacity changes Frequency drift due to variations in tempera-' as above pointed out which are caused by temture is particularly noticeable in superheteroperature variations is substantially corrected. dyne circuits where the tuning is of the prede- I claim:

termined type which is operated bymeans of a. 1. A compensating capacitor comprising two telephone type dial, push buttons or the like, metal plates, an insulator therebetween, and so that for a given station, all the tuning elemeans for holding the plates in juxtaposition, ments are given predetermined settings. Except one of said plates being curved spherically and for the frequency drifts referred to the set would made of bimetal adapted to change its curvature 40 then be tuned for the given frequency. Diflerand hence the capacitance of the capacitor with ences in temperature however cause the set to ltferences in temperature. drift from the desired frequency and this drift 2. A compensating capacitor comprising two is mainly in the oscillator stage and this drift metal plates, a solid insulator therebetween, and can be substantially corrected for in that stage a bolt extending centrally therethrough for holdalone. ing the plates in juxtaposition, one of said plates 5 The embodiment illustrated comprises a. combeing curved spherically, the curved plate being pensatlng capacitor which may be placed in a adapted to change its curvature with respect to radio circuit to compensate for temperature varthe other plate with differences in temperature lotions. This capacitor comprises a metal disk whereby the capacitance of the capacitor will H and a bimetal disk 52 separated by a disk of change.

suitable dielectric material Hi all held together 50 E 11"? 

